Among nonvolatile memory devices, the resistive random access memory (ReRAM) includes a memory element section constituted by a two-terminal structure in which a variable resistance layer is sandwiched between two electrodes. The structure of this memory element section is simple and superior in scalability. Furthermore, the resistive random access memory has a low driving voltage. Thus, the resistive random access memory is expected for applications such as a substitute for the NAND flash memory, which is widely applied to commercial products as a high-capacity semiconductor memory element.
As a material of the variable resistance layer, various substances such as transition metal oxides, sulfides, perovskite oxides, and semiconductors are investigated. Among them, in a nonvolatile memory device, a semiconductor such as amorphous silicon can be used as a material of the variable resistance layer. Such a nonvolatile memory device has a high affinity for the manufacturing process of silicon-based CMOS (complementary metal oxide semiconductor). Furthermore, in this variable resistance layer, the nonvolatile memory operation with low current has been demonstrated.
In such a nonvolatile memory device, improvement of data retention characteristics is important.